1. Field of the Invention
The present invention relates generally to wireless telecommunication systems, and in particular relates to the use of a holographic optical element (HOE) device in an optical wireless telecommunication system receiver.
2. Background Information
At a basic level, a typical optical wireless telecommunications system comprises an optical transmitter and an optical receiver, with associated electronics to modulate and demodulate data on a light beam. Often, receivers are basically telescopes.
An example of a configuration of a typical receiver system is shown at 10 in FIG. 1. The system 10 comprises a cylindrical receiver tube 12 with a lens and cover 14 (typically made of glass) at one end, and system of internal mirrors to collect and focus light to a single receiving point. In this system 10, a light beam 16 enters the receiver tube 12, and is collected using internal mirrors, including a mirror 18 and a spherical mirror 20. Finally, the mirrors 18 and 20 focus the light beam 16 onto the single receiving point at a photodetector 22. An example of such a traditional system is a Cassegrain telescope with detector electronics replacing the eyepiece.
The various optics and components for the system 10 are heavy, fragile, bulky, difficult to manufacture with consistent quality, and expensive. Because optical communications systems are capable of much higher data rates than traditional radio frequency (RF) systems, the ability to make stable and inexpensive systems is becoming more and more desirable.
According to an aspect of the invention, a system includes a holographic optical element (HOE) device. The HOE device has a first element having first and second surfaces, with the first surface being positionable to face incident light rays. An emulsion material having an interference pattern recorded thereon is disposed over the second surface of the first element. A second element has a first surface disposed over the emulsion material, and is structured to pass resulting light rays, derived from the incident light rays diffracted by the interference pattern, in a direction towards a location facing a second surface of the second element. An optical processing unit receives the resulting light rays.